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  • 1. Albertson, F.
    et al.
    Boden, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Gilbert, J.
    Comparison of different methods to couple nonlinear source descriptions in the time domain to linear system descriptions in the frequency domain - Application to a simple valveless one-cylinder cold engine2006In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 291, no 05-mar, p. 963-985Article in journal (Refereed)
    Abstract [en]

    In duct acoustics the fundamental sound generating mechanisms must often be described by nonlinear time domain models. A linear frequency domain model is in many cases sufficient for describing the sound propagation in the connected duct system. This applies both for fluid machines such as IC-engines and compressors and for musical wind instruments. Methods for coupling a nonlinear source description to a linear system description have been proposed by several authors. In this paper some of those methods are compared concerning accuracy, calculation time and the possibility to perform parametric studies. The model problem used is a simple piston-restriction system connected to a linear system with varying complexity. The piston and restriction are considered as the source part and are modelled nonlinearly.

  • 2.
    Allam, Sabry
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Helwan University, Egypt.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Methods for Accurate Determination of Acoustic Two-Port Data in Flow Ducts2005In: 12th International Congress on Sound and Vibration 2005: ICSV 2005, 2005Conference paper (Other academic)
    Abstract [en]

    Measurement of plane wave acoustic transmission properties, so called two-port data, of flow duct components is important in many applications. It is an important tool for instance in the development of mufflers for IC-engines. Accurate measurement of the acoustic two port data can be used not only to determine the transmission loss but also to determine physical properties like flow resistivty as well as speed of sound and impedance. Measurement of two-port data is difficult when the flow velocity in the measurement duct is high because of the flow noise contamination of the measured pressure signals. Techniques to improve the acoustic two-port determination have been tested in this paper. A number of possible configurations for connecting loudspeakers to the flow duct have been investigated. It was found that using a perforate pipe section with about 50% porosity between the loudspeaker side branch and the duct gave the best signal-to-noise ratio out of the studied configurations. Different signal processing techniques have been tested for reducing the adverse effects of flow noise at the microphones. The most successful techniques require a reference signal which can be either the electric signal being input to the loudspeakers or one of the microphone signals. As a reference technique stepped sine excitation with cross-spectrum based frequency domain averaging was used. This technique could give good results for most cases. Using a periodic signal (saw-tooth) and synchronised time domain averaging good results could be obtained if a sufficient number of averages was used. At flow velocities higher than M=0.2 about 10000 averages were needed. Random excitation together with cross-spectrum based frequency domain averaging also gave good result if the same number of averages was used. Ordinary frequency domain averaging is not sufficient at high flow velocities. It was also shown that using cross-spectrum based frequency domain averaging an improvement could be obtained if the microphone with the highest signal-to-noise ratio at each frequency was used as the reference microphone rather than a fixed microphone.

  • 3.
    Allam, Sabry
    et al.
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Bodén, Hans
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Signal to noise ratio enhancement methods in acoustic flow duct measurements2004In: ICSV12-St Petersburg, 2004Conference paper (Other academic)
  • 4.
    Allam, Sabry
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Over-determination in acoustic two-port data measurement2006In: ICSV13-Vienna / [ed] J. Eberhardsteiner, H.A. Mang, H. Waubke, 2006Conference paper (Other academic)
    Abstract [en]

    Measurement of plane wave acoustic transmission properties, so called two-port data, of flow duct components is important in many applications. It is an important tool for instance in the development of mufflers for IC-engines. Measurement of two-port data is difficult when the flow velocity in the measurement duct is high because of the flow noise contamination of the measured pressure signals. The plane wave acoustic two-port is a 2x2 matrix containing 4 complex quantities at each frequency. To experimentally determine these unknowns the acoustic state variables on the inlet and outlet side must be measured for two independent test cases. The two independent test cases can be created by: changing the acoustic load on the outlet side leading to the so-called two-load technique or by using one acoustic source on the inlet side and one acoustic source on the outlet side leading to the so-called two-source technique. In the latter case the independent test cases are created by first using the source on the inlet side and then the source on the outlet side. As pointed out by Åbom it is also possible to run both sources simultaneously to create more than two independent test cases. This over-determination could be used to improve the measurement results for instance if the data is contaminated by flow-noise. In this paper over-determination is tested by applying up to 5 different test cases. This procedure has been applied to a single orifice test object.

  • 5.
    Allam, Sabry
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Knutsson, M.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Development of acoustic models for high frequency resonators for turbocharged IC-engines2012In: SAE Technical Paper 2012-01-1559, 2012, 2012Conference paper (Refereed)
    Abstract [en]

    Automotive turbo compressors generate high frequency noise in the air intake system. This sound generation is of importance for the perceived sound quality of luxury cars and may need to be controlled by the use of silencers. The silencers usually contain resonators with slits, perforates and cavities. The purpose of the present work is to develop acoustic models for these resonators where relevant effects such as the effect of a realistic mean flow on losses and 3D effects are considered. An experimental campaign has been performed where the two-port matrices and transmission loss of sample resonators have been measured without flow and for two different mean flow speeds. Models for two resonators have been developed using 1D linear acoustic theory and a FEM code (COMSOL Multi-physics). For some resonators a separate linear 1D Matlab code has also been developed. Different models, from the literature, for including the effect of mean flow on the acoustic losses at slits and perforates have been implemented in the codes and compared to the experimental data. Correct modeling of acoustic losses for resonators with complicated geometry is important for the simulation and development of new and improved silencers, and the present work contributes to this understanding. The developed models give acceptable agreement with the measured results even with flow but can be improved for 3D FEM if correct CAD data is available. The 1D linear theory can be used for simple geometries and to get a general overview related to the resonance frequencies and damping level.

  • 6.
    Boden, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    IC-Engine Exhaust and Intake System Acoustic Source Characterization2014In: SAE International Journal of Engines, ISSN 1946-3936, E-ISSN 1946-3944, Vol. 7, no 3, p. 1579-1584Article in journal (Refereed)
    Abstract [en]

    The paper gives an overview of techniques used for characterization of IC-engines as acoustic sources of exhaust and intake system noise. Some recent advances regarding nonlinear source models are introduced and discussed. To calculate insertion loss of mufflers or the level of radiated sound information about the engine as an acoustic source is needed. The source model used in the low frequency plane wave range is often the linear time invariant one-port model. The acoustic source data is obtained from experimental tests or from 1-D CFD codes describing the engine gas exchange process. The IC-engine is a high level acoustic source and in most cases not completely linear. It is therefore of interest to have models taking weak non-linearity into account while still maintaining a simple method for interfacing the source model with a linear frequency domain model for the attached exhaust or intake system. The use of source characterization in acoustic design of mufflers is also briefly discussed.

  • 7.
    Boden, Hans
    et al.
    KTH, Superseded Departments, Vehicle Engineering.
    Albertson, F.
    Linearity tests for in-duct acoustic one-port sources2000In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 237, no 1, p. 45-65Article in journal (Refereed)
    Abstract [en]

    Acoustic one-port source data are commonly used to predict the plane wave sound generation in duct and pipe systems connected to fluid machines. The source data are usually determined experimentally, which assumes that linear time-invariant system theory can be used. Since some machines such as IC-engines and compressors generate very high sound levels in the connecting ducts or pipes it is of interest to investigate whether the assumption of linearity is justified. Linearity tests for linear system identification when both input and output signals can be measured are common in the literature. In the case when only the output signal can be measured linearity tests are not so readily found. This paper presents two different linearity coefficients for determining whether an acoustic one-port source under test is linear. Their sensitivity to random noise and their ability to detect non-linearities are investigated by simulations and measurements on several types of machines.

  • 8.
    Boden, Hans
    et al.
    KTH, Superseded Departments, Vehicle Engineering.
    Sarin, S.
    Aeroacoustic research in Europe: The CEAS-ASC report on 1999 highlights2000In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 237, no 3, p. 477-482Article in journal (Refereed)
    Abstract [en]

    This paper is a report on the highlights of aeroacoustics research and development in Europe in 1999, compiled from the information provided to the Aeroacoustics Specialists Committee (ASC) of the Confederation of European Aerospace Societies (CEAS). CEAS presently comprises the national Aerospace Societies of France (AAAF), Germany (DGLR), Italy (AIDAA), The Netherlands (NVvL), Spain (AIAE), Sweden (FTEF), Switzerland (SVFW) and the United Kingdom (RaeS).

  • 9.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Acoustic characterisation of perforates using non-linear system identification techniques2007In: 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), American Institute of Aeronautics and Astronautics, 2007Conference paper (Refereed)
    Abstract [en]

    This paper discusses the use of nonlinear system identification techniques for determination of linear acoustic impedance and non-linear acoustic properties of perforates and other facing sheets used in aircraft engine liners.

  • 10.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Acoustic properties of perforates under high level multi-tone excitation2013In: 19th AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2013Conference paper (Refereed)
    Abstract [en]

    This paper discusses the effect of high level multi-tone acoustic excitation on the acoustic properties of perforates. It is based on a large experimental study of the nonlinear properties of these types of samples without mean grazing or bias flow. Compared to previously published results the present investigation concentrates on the effect of multiple harmonics. It is known from previous studies that high level acoustic excitation at one frequency will change the acoustic impedance of perforates at other frequencies, thereby changing the boundary condition seen by the acoustic waves. This effect could be used to change the impedance boundary conditions and for instance increase the absorption. It could obviously also pose a problem for the correct modelling of sound transmission through ducts lined with such impedance surfaces. Experimental results are compared to a quasi-stationary model. The effect of the combination of frequency components and phase in the excitation signal is studied.

  • 11.
    Bodén, Hans
    KTH, Superseded Departments, Vehicle Engineering.
    APPLICATION OF LINEAR ACOUSTIC SOURCE DATA MEASUREMENT TECHNIQUES FOR TRUCK DIESEL ENGINES2004In: ICSV12-St Petersburg, 2004Conference paper (Other academic)
    Abstract [en]

    IC-engines are known from previous studies to be non-linear sources of exhaust system noise. Never the less linear frequency domain prediction codes are used for calculation of low frequency sound transmission in and sound radiation from IC-engine exhaust systems. To calculate insertion loss of mufflers or the level of radiated sound information about the engine as an acoustic source is needed. The source model used in the low frequency plane wave range is the linear time invariant 1-port model. The acoustic source data is usually obtained from experimental tests where multi-load methods and especially the two-load method are most commonly used. In this paper results from experiments on truck Diesel engines are presented. A number of different techniques for extracting source data are tested and the linearity and time invariance is investigated. The results show that a linear time-invariant model can provide good results.

  • 12.
    Bodén, Hans
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Determination of flow resistance from acoustic in-duct measurements 2004In: Collection of Technical Papers - 10th AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2004, p. 494-504Conference paper (Refereed)
    Abstract [en]

    This paper discusses the use of acoustic measurement techniques for determination of non-linearity and flow resistance of perforates and other facing sheets used in aircraft engine liners. Impedance measurements with pure tone excitation and random noise excitation are discussed as well as a non-linear system identification technique.

  • 13.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Determination of the acoustic properties of liners under high level multi-tone excitation2016In: 22nd AIAA/CEAS Aeroacoustics Conference, 2016, 2016Conference paper (Refereed)
    Abstract [en]

    This paper discusses the effect of high level multi-tone acoustic excitation on the acoustic properties of acoustic liners and perforates. It is based on an experimental study of the nonlinear properties of these types of samples without mean grazing or bias flow. Compared to previous studies results from normal incidence impedance tube measurements are compared to liners placed in a grazing incidence configuration. It is known from previous studies that high level acoustic excitation at one frequency will change the acoustic impedance of perforates at other frequencies, thereby changing the boundary condition seen by the acoustic waves. This effect could be used to change the impedance boundary conditions and for instance increase the absorption. It could also pose a problem for the correct modelling of sound transmission through ducts lined with such impedance surfaces. The effect of the combination of frequency components is also studied. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

  • 14.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Experimental investigation of harmonic interaction effects for perforates2005In: Collection of Technical Papers: 11th AIAA/CEAS Aeroacoustics Conference, Monterey, CA, 2005, Vol. 2, p. 1236-1242Conference paper (Refereed)
    Abstract [en]

    This paper presents the results of a small experimental study of acoustic non-linear harmonic interaction effects for perforates. Impedance measurements using multiple pure tone excitation has been used. The results are potentially of interest for perforates and other facing sheets used in aircraft engine liners as well as perforate pipes used in automotive mufflers. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

  • 15.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Experimental source characterization techniques for studying the acoustic properties of perforates under high level acoustic excitation2011In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 130, no 5, p. 2639-2647Article in journal (Refereed)
    Abstract [en]

    This paper discusses experimental techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristic. The methods developed are intended both for studies of non-linear energy transfer to higher harmonics for samples only accessible from one side such as wall treatment in aircraft engine ducts or automotive exhaust systems and for samples accessible from both sides such as perforates or other top sheets. When harmonic sound waves are incident on the sample nonlinear energy transfer results in sound generation at higher harmonics at the sample (perforate) surface. The idea is that these sources can be characterized using linear system identification techniques similar to one-port or two-port techniques which are traditionally used for obtaining source data for in-duct sources such as IC-engines or fans. The starting point will be so called polyharmonic distortion modeling which is used for characterization of nonlinear properties of microwave systems. It will be shown how acoustic source data models can be expressed using this theory. Source models of different complexity are developed and experimentally tested. The results of the experimental tests show that these techniques can give results which are useful for understanding non-linear energy transfer to higher harmonics.

  • 16.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    In-duct source characterization for multiple sources2009In: 16th International Congress on Sound and Vibration 2009, ICSV 2009, 2009, p. 2664-2671Conference paper (Refereed)
    Abstract [en]

    This paper discusses experimental techniques for detecting if there are multiple sources in a duct and obtaining the acoustic characteristics of these sources. Experimental techniques for in-duct source characterization under plane wave conditions in ducts, when we know the location of the source, are well established. In some cases there can however be sources at both ends of a duct. The paper starts with discussing the possibility to, by using a number of flush mounted microphones in the duct, detect sources located on both sides of the test section and to extract the acoustic source characteristics of the sources. First the sound field in a duct with sources at both ends is discussed and described. The theory for experimental determination of source data is then described. A discussion of the consequences of source correlation is included. The methods are first tested using loudspeakers in a duct.

  • 17.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    International Journal of Aeroacoustics, volume 6, number 12007Collection (editor) (Refereed)
    Abstract [en]

    In November 2005 a Workshop with the title ”Active Control of Aircaft Noise – Concept to Reality” was organised by CEAS-ASC (Council of European Aeronautical Societies – Aeroacoustics Specialist Committee). The Workshop was held at KTH (the Royal Institute of Technology) in Stockholm, Sweden and was chaired by Hans Bodén from KTH and Urban Enborg from A2 Acoustics. This was the ninth in a series of annual Workshops organised by CEAS-ASC. It was co-sponsored by_the American Insitute of Aeronautics and Astronautics (AIAA), CARAN SAAB Engineering, SAAB, Airbus, KTH and the EU through the X2-Noise Thematic Network.

                A total of 20 papers were presented during the two day event divided into four sessions: interior noise, airframe noise flow control, jet noise and fan noise.

                The aim of the Workshop was to summarise the state of the art and to indentyfy breakthroughs needed in order to apply active control in reducing aircraft noise. The technique is most mature in control of interior noise where there are 850 systems flying in regional turnoprop aircraft , business turboprop and some jet aircraft and military aircraft. There has been a lot of work on active control of fan noise both on active liners and using flow control to reduce fan tone noise and active control of buzz saw noise. Also for airframe noise there have been studies e.g., on applying active flow control to highlift devices. Closed-loop flow control has been used in control of cavity tones. Studies have also been made of the use of flow injection for reduction of jet noise. Another technique tested for jet noise reduction is deployable chevrons.

    The present issue contains five of the twenty papers presented at he Workshop. The selection is slanted towards active control of fan noise with two papers on the interesting subject of buzz saw noise reduction, one paper on control of fan tone noise using flow induction and one paper on hybrid passive/active treatment for inlet nacelles. In addition, there is one paper on optimisation of interior noise control.

  • 18.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Multi-port techniques for acoustic characterisation of non-linear in-duct discontinuities2009In: 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), 2009Conference paper (Refereed)
    Abstract [en]

    This paper discusses techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics such as perforates and other facing sheets used in aircraft engine liners and automotive mufflers. It is assumed that the non-linearity occurs locally at constrictions or sharp corners. Multi-port techniques using sinusoidal excitation for better characterization of samples with non-linear properties are developed and experimentally tested. These new techniques take non-linear energy transfer between sound field harmonics into account.

  • 19.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Nonlinear source characterisation techniques for IC-engines2012In: 19th International Congress on Sound and Vibration 2012, ICSV 2012, 2012, p. 2442-2449Conference paper (Refereed)
    Abstract [en]

    A source characterization model for IC-engines, which can take weakly nonlinear source properties into account, is developed in the paper. It is based on so called polyharmonic distortion modeling, used for nonlinear characterization of microwave systems. Comparisons are made with the results from linear source models and another previously published weakly nonlinear source model. The results show that the new nonlinear impedance matrix model gives improvements in the prediction of sound pressure levels in the exhaust system.

  • 20.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Vibration monitoring.
    Non-linear system identification techniques for determination of the acoustic properties of perforates2015In: 21st AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2015Conference paper (Refereed)
    Abstract [en]

    This paper discusses the use of nonlinear system identification techniques for determination of linear acoustic impedance and non-linear acoustic properties of perforates and other facing sheets used in aircraft engine liners. Multiple input single output nonlinear system identification techniques are revisited and applied to the problem of nonlinear acoustic characterisation of perforates. Bi-linear signal analysis techniques are also tested as well as Hilbert transform techniques applicable for non-stationary and nonlinear problems. It is shown that random excitation nonlinear system identification techniques have the potential of identifying and characterising non-linear acoustic properties of these types of samples.

  • 21.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    On impedance measurements for samples with non-linear acoustic properties2008In: 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference), Vancouver, BC, 2008Conference paper (Refereed)
    Abstract [en]

    This paper discusses techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics such as perforates and other facing sheets used in aircraft engine liners and automotive mufflers. It is assumed that the non-linearity occurs locally at constrictions or sharp corners. The paper starts with a short review of previous impedance tube measurements made for determining the acoustic impedance of non-linear samples. Multi-port techniques using sinusoidal excitation for better characterization of samples with non-linear properties are developed and experimentally tested.

  • 22.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    One-sided multi-port techniques for characterisation of in-duct samples with nonlinear acoustic properties2012In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 331, no 13, p. 3050-3067Article in journal (Refereed)
    Abstract [en]

    Single sided multi-port system identification techniques, using sinusoidal excitation, for studying nonlinear energy transfer to higher harmonics for samples only accessible from one side such as perforated liners used as wall treatment in aircraft engine ducts are presented. The starting point is the so called polyharmonic distortion theory used for studying microwave systems. Models of different level of complexity are developed and the system identification results are compared. Experimental results, including error analysis, for a perforate sample are presented. The use of these techniques for analysing nonlinear energy transfer to higher harmonics and to improve the understanding of the physical phenomena involved are illustrated.

  • 23.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Polyharmonic distortion modelling applied to acoustic characterisation of peforates2011In: 17th AIAA/CEAS Aeroacoustics Conference 2011 (32nd AIAA Aeroacoustics Conference), 2011Conference paper (Refereed)
    Abstract [en]

    This paper discusses the possibility to apply polyharmonic distortion modelling, used for nonlinear characterisation of microwave systems, to acoustic characterisation of samples with non-linear properties such as perforates and other facing sheets used in aircraft engine liners and automotive mufflers. In some previous papers multi-port techniques using sinusoidal excitation for characterization of samples with non-linear properties were developed and experimentally tested. These techniques aimed at taking non-linear energy transfer between sound field harmonics into account. Essentially linear system identification theory was however used assuming that superposition applies and that the functions studied are analytical. Polyharmonic distortion modelling does not assume that the function relating waves incident and reflected or transmitted is analytic nor does it assume application of normal superposition. This technique is tested on experimental data obtained from measurements on a perforate mounted in a duct. The similarity to the previously developed nonlinear scattering matrix techniques is demonstrated. It is shown how the results obtained can be used to analyse nonlinear energy transfer to higher harmonics. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

  • 24.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Recent Advances In  IC-engine acoustic source Characterisation2007In: 14th International Congress on Sound and Vibration (ICSV14), 2007Conference paper (Other academic)
    Abstract [en]

    This paper summarizes work performed at KTH over the years on source characterization for IC-engine exhaust and intake systems. An overview is made of recent advances in experimental and simulation methods for determination of acoustic source data. These include a source model which can consider weakly non-linear sources and application of 1-D CFD codes for extracting source data. Examples are presented for both exhaust and intake systems and for different types of engines. The results show that reasonably accurate results can be obtained using 1-D CFD codes to extract acoustic source data and that the newly developed non-linear multi-load technique has got advantages over the traditional two-load technique for determining source data from experiments.

  • 25.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Single tone excitation techniques for determination of non-linear acoustic properties of perforates2010In: Proceedings of the International Conference on Noise and Vibration Engineering, ISMA 2010, 2010, p. 597-609Conference paper (Refereed)
    Abstract [en]

    This paper discusses experimental techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics. The methods developed are intended for studies of non-linear energy transfer to higher harmonics for samples such as perforates or other material used as top sheets in aircraft engine liners and automotive mufflers. New single sided and double sided multi-port techniques, using sinusoidal excitation, for characterisation of samples with non-linear properties are developed and experimentally tested.  The results of the preliminary experimental tests show that these new techniques can give results which are useful for understanding non-linear energy transfer to higher harmonics.

  • 26.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Study of nonlinear energy transfer for perforated wall treatment using acoustic source characterisation techniques2011In: 18th International Conference on Sound and Vibration (ICSV18), 2011Conference paper (Other academic)
    Abstract [en]

    This paper discusses experimental techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics such as perforates used in aircraft engine liners and automotive mufflers. The methods developed are intended for studies of non-linear energy transfer to higher harmonics for samples only accessible from one side such as wall treatment in aircraft engine ducts or automotive exhaust systems. Nonlinear energy transfer results in sound generation at higher harmonics at the sample (perforate) surface. The idea here is that these sources can be characterised using linear one-port techniques which are traditionally used for obtaining source data for in-duct sources such as fans or IC-engines. The results of the experimental tests show that these new techniques can give results which are useful for understanding non-linear energy transfer to higher harmonics.

  • 27.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    The effect of high level multi-tone excitation on the acoustic properties of perforates and liner samples2012In: 18th AIAA/CEAS Aeroacoustics Conf. (33rd AIAA Aeroacoustics Conf.), American Institute of Aeronautics and Astronautics, 2012Conference paper (Refereed)
    Abstract [en]

    This paper discusses the effect of high level multi-tone acoustic excitation on the acoustic properties of perforates and liner samples. It is based on a large experimental study of the nonlinear properties of these types of samples without mean grazing or bias flow. It is known from previous studies that high level acoustic excitation at one frequency will change the acoustic impedance of perforates at other frequencies, thereby changing the boundary condition seen by the acoustic waves. This effect could be used to change the impedance boundary conditions and for instance increase the absorption. It could obviously also pose a problem for the correct modelling of sound transmission through ducts lined with such impedance surfaces. First a quasi-stationary model for the acoustic properties of the perforate is discussed and the results are compared to experimental data. The effect of the combination of frequency components in the excitation signal is studied to find out if it matters if we are using tones which are harmonically related or not. The effect the phase of the frequency components is studied using both the model and experimental data. It is also discussed if a parameter controlling the impedance can be found for an arbitrary combination of tones with different frequencies.

  • 28.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    The effect of speed variation on in-duct source data determination2014In: 21st International Congress on Sound and Vibration 2014, ICSV 2014, 2014, p. 2395-2401Conference paper (Refereed)
    Abstract [en]

    Experimental acoustic source characterization is used for IC-engines and fluid machines connected to duct or pipe systems. Information about the engine as an acoustic source is needed to calculate insertion loss of mufflers or the level of radiated sound. The source model used in the low frequency plane wave range is often the linear time invariant 1 -port model. The acoustic source data is obtained from experimental tests or from 1 -D CFD codes describing the engine gas exchange process. Multi-load methods and especially the two-load method are most commonly used to extract the source data. The IC-engine is a high level acoustic source and in most cases not completely linear. The real part of the measured source impedance sometimes has negative values which is un-physical. This effect has been attributed to non-linearity and source time variation. Another possible explanation could be speed variation giving measurement errors especially for higher harmonics. In the present paper this effect is studied by re-visiting source data experiments for IC-engine exhausts and comparing the outcome of different methods for extracting the amplitude and phase of the pressure in terms of frequency components or engine orders.

  • 29.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Two-Port Techniques For Characterisation Of Non-Linear In-Duct Sources2008In: 15th International Congress on Sound and Vibration (ICSV15), 2008Conference paper (Other academic)
    Abstract [en]

    This paper discusses techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics such as perforates and other facing sheets used in aircraft engine liners and automotive mufflers.  It is assumed that the non-linearity occurs locally at constrictions or sharp corners. Non-linear wave propagation and wave steepening are not taken into account. The paper starts with a review of previous impedance tube measurements made for determining the acoustic impedance of non-linear samples. The effect of using different types of excitation and non-linear harmonic interaction mechanisms are discussed. Experiments were previously made using both pure tone and random excitation and the relevant parameters controlling the non-linearity were discussed. A study of harmonic interaction effects using two-tone excitations was made and later extended to multi-tone excitation for different types of perforates. In the linear case the impedance is independent of the sound field but when the sound pressure level is high the perforate impedance will be dependent on the acoustic particle velocity in the holes. For pure tone excitation it is usually assumed that the impedance will be controlled by the acoustic particle velocity at that frequency, even though the non-linearity will in fact cause energy to be transferred to other frequencies. If the acoustic excitation is random or periodic with multiple harmonics the impedance at a certain frequency may depend on the particle velocity at other frequencies. The results show that the total rms-value of the particle velocity in the holes seems to be the relevant parameter controlling the non-linearity. A study was previously made of using non-linear system identification techniques for this purpose. Multi-port techniques using sinusoidal excitation for better characterization of samples with non-linear properties are developed in the present paper. These new techniques take the non-linear energy transfer into account. 

  • 30.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Two-sided multi-port techniques for characterisation of in-duct samples with non-linear acoustic properties2013In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 99, no 3, p. 359-378Article in journal (Refereed)
    Abstract [en]

    This paper discusses experimental techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics. The methods developed are intended for studies of non-linear energy transfer to higher harmonics for samples accessible from both side such as perforates or other material used as top sheets in aircraft engine liners and automotive mufflers. New double sided multi-port techniques, using sinusoidal excitation, for characterisation of samples with non-linear properties are developed and experimentally tested. The results of the experimental tests show that these new techniques can give results which are useful for understanding non-linear energy transfer to higher harmonics.

  • 31.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Allam, Sabry
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Holmberg, Andreas
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Experimental Techniques for Aeroacoustics in Low Mach Number Confined Flows: Keynote Paper2011In: Proceedings of the International Conference on Mechanical Engineering 2011(ICME2011) 18-20 December 2011, Dhaka, Bangladesh, ICME , 2011Conference paper (Other academic)
    Abstract [en]

    Measurement of plane wave acoustic transmission properties, so called two-port data, of flow duct components is important in many applications such as in the development of mufflers for IC-engines. Measurement of two-port data is difficult when the flow velocity in the measurement duct is high because of the flow noise contamination of the measured pressure signals. The wall mounted pressure transducers normally used will pick up unwanted flow noise mainly in the form of turbulent pressure fluctuations. The problem is then obtaining a signal-to- noise ratio high enough for quality measurements. Techniques to improve acoustic two-port determination have been developed in this paper, including test rig design, signal processing techniques and over-determination.

  • 32.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Aslan, Johan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Yousif, Michel
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    A study of annoyance caused by ground based activities at Bromma airport2010In: 17th International Congress on Sound and Vibration (ICSV17), 2010Conference paper (Other academic)
    Abstract [en]

    Bromma airport is located nearby the city centre of Stockholm Sweden. There are a number of residential areas around the airport. The paper reports results from a measurement campaign and a questionnaire survey investigation among the people living in the area Bromma kyrka, located approximately 500 meters from the airport. The objective of the study was to identify the most annoying sound sources related to ground activities at the airport. This means that the noise events caused by starting and landing airplanes were identified using information from the airport, so that they could be separated from the noise caused by ground based activities. The survey showed that the most annoying ground based noise sources within the airport wee, airplane warm ups and airplane taxiing. Starting and landing airplanes were also important source of annoyance. The most important source of noise annoyance from outside the airport boundaries was road traffic. The results from the survey were compared with the measured noise levels giving reasonable correlation between recorded high noise level events and logged annoyance events.

  • 33.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Cordioli, J. A.
    Spillere, A. M.
    Effect of flow direction on acoustic liner impedance measurement results2016In: ICSV 2016 - 23rd International Congress on Sound and Vibration: From Ancient to Modern Acoustics, 2016Conference paper (Refereed)
    Abstract [en]

    The last twenty years have seen a large development in inverse techniques for the determination of liner impedance under grazing flow conditions, so called impedance eduction techniques. This paper contributes to a continuing effort to gain confidence in results obtained under different acoustical excitation configurations. Many test rigs for determination of liner impedance including the effect of mean flow use plane wave excitation on the upstream side of the liner. Some studies has compared the result for downstream acoustic excitation and found that different acoustic impedances are obtained in the two cases. It is still an open question if this result is due to the application of the Ingard-Myers boundary condition or to other errors or flaws in the measurements. This paper collects data available in the literature to see if the trend of obtaining different results for upstream and downstream excitation is persistent.

  • 34.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Aeroacoustics research in Europe: The CEAS-ASC report on 2012 highlights2013In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 332, no 25, p. 6617-6636Article, review/survey (Refereed)
    Abstract [en]

    The Council of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee (ASC) supports and promotes the interests of the scientific and industrial aeroacoustics community on an European scale and European aeronautics activities internationally. In this context, "aeroacoustics" encompasses all aerospace acoustics and related areas. Each year the committee highlights some of the research and development projects in Europe. This paper is a report on highlights of aeroacoustics research in Europe in 2012, compiled from information provided to the ASC of the CEAS. During 2012, a number of research programmes involving aeroacoustics were funded by the European Commission. Some of the highlights from these programmes are summarized in this paper, as well as highlights from other programmes funded by national programmes or by industry. Enquiries concerning all contributions should be addressed to the authors who are given at the end of each subsection.

  • 35.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Eslami, Armin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Determination of non-linear acoustic properties of perforates using single tone excitation2010In: 17th International Congress on Sound and Vibration (ICSV17), 2010Conference paper (Other academic)
    Abstract [en]

    This paper discusses experimental techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics. The methods developed are intended for studies of non-linear energy transfer to higher harmonics for samples accessible from both side such as perforates or other material used as top sheets in aircraft engine liners and automotive mufflers. New double sided multi-port techniques, using sinusoidal excitation, for characterisation of samples with non-linear properties are developed and experimentally tested.  The results of the preliminary experimental tests show that these new techniques can give results which are useful for understanding non-linear energy transfer to higher harmonics.

  • 36.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Guo, Ying
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Tözün, Hüseyin Bora
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Experimental investigation of nonlinear acoustic properties for perforates2006In: Collection of Technical Papers: 12th AIAA/CEAS Aeroacoustics Conference, Cambridge, MA, 2006, Vol. 1, p. 67-74Conference paper (Refereed)
    Abstract [en]

    This paper presents the results of a study of non-linear acoustic properties of perforates and micro-perforates. The results are potentially of interest for perforates and other facing sheets used in aircraft engine liners as well as perforate pipes used in automotive mufflers. In the linear limit the perforate acoustic impedance is independent of the sound field but when the sound pressure level is high it will be dependent on the acoustic particle velocity in the holes. For pure tone excitation the impedance will be controlled by the acoustic particle velocity at that frequency. If the acoustic excitation is random or periodic with multiple harmonics the impedance at a certain frequency will depend on the particle velocity at other frequencies. In this paper a study lias been made of harmonic interaction effects by using multiple pure tone excitation and random noise excitation.

  • 37.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Guo, Ying
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Tözün, Hüseyin Bora
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Investigation of Nonlinear Acoustic properties for Perforates2006In: ICSV13-Vienna / [ed] J. Eberhardsteiner, H.A. Mang, H. Waubke, 2006Conference paper (Other academic)
    Abstract [en]

    This paper presents the results of a study of non-linear acoustic properties of perforates and micro-perforates. The results are potentially of interest for perforates and other facing sheets used in aircraft engine liners as well as perforate pipes used in automotive mufflers. In the linear limit the perforate acoustic impedance is independent of the sound field but when the sound pressure level is high it will be dependent on the acoustic particle velocity in the holes. For pure tone excitation the impedance will be controlled by the acoustic particle velocity at that frequency. If the acoustic excitation is random or periodic with multiple harmonics the impedance at a certain frequency will depend on the particle velocity at other frequencies. In this paper a study has been made of harmonic interaction effects by using multiple pure tone excitation and random noise excitation.

  • 38.
    Bodén, Hans
    et al.
    KTH, Superseded Departments, Vehicle Engineering.
    Tonsa, M.
    AVL.
    Fairbrother, R.
    AVL.
    On extraction of IC-engine linear acoustic source data from non-linear simulations2004In: ICSV12-St Petersburg, 2004Conference paper (Other academic)
    Abstract [en]

    Linear frequency domain prediction codes are used for calculation of low frequency sound transmission in and sound radiation from IC-engine exhaust systems. To calculate insertion loss of mufflers or the level of radiated sound information about the engine as an acoustic source is needed. The source model used in the low frequency plane wave range is the linear time invariant 1-port model. The acoustic source data is usually obtained from experimental tests where multi-load methods and especially the two-load method are most commonly used. These tests are time consuming and expensive. It would therefore be of interest to extract the acoustic source data from existing 1-D CFD codes describing the engine gas exchange process. In this paper a comparison is made between results obtained applying the two-load technique to measurements on a truck Diesel engine and to 1-D CFD simulations of the same engine. The results show that it is possible to obtain reasonably accurate source data estimates from the simulations.

  • 39.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Torregrosa, A.
    Ollivier, F.
    Peat, K.
    Fairbrother, R.
    Henriksson, B.
    Recouvreur, P.
    Poullard, O.
    Glav, Ragnar
    Scania AB, Sweden.
    Lavrentjev, J.
    Noise from turbo-charged diesel engine exhaust systems2005In: 12th International Congress on Sound and Vibration 2005: ICSV 2005, 2005, p. 2231-2238Conference paper (Refereed)
    Abstract [en]

    This paper summarises the main results of an EU-funded research project, ARTEMIS (G3RD-CT-2001-00511), on noise from turbo-charged Diesel engine exhaust systems. The project started in September 2001 and ended in August 2004 and was co-ordinated by KTH. The project had 10 partners from 6 different European countries, 5 universities and 5 companies including some major truck and car manufacturers. The main objective was to develop new and improved computational tools for predicting noise from exhaust systems. New models for describing the engine as an acoustic source were developed and experimentally tested. They include a linear time-varying source model and a non-linear frequency domain model. Linear time-invariant source data was also determined both from experiments and using 1-D gas-exchange simulations. New and improved models were developed for the turbo-group including non-linear time domain models and a linear time-varying model. New models were developed and experimentally tested for sound transmission through the Diesel particulate filter included in modern Diesel engine after-treatment devices. Improved models were developed for describing perforate mufflers with high mean flow velocities. Improved experimental techniques for determination of transmission properties of duct system components were developed. Models were developed and coded for sound reflection and radiation from tailpipe openings. Full experimental validation of the Munt theory for radiation from open pipes with flow was produced. In conclusion it can be said that the project was successful and gave many useful results.

  • 40.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Zhou, L.
    Cordioli, J. A.
    Medeiros, A. A.
    Spillere, A. M. N.
    On the effect of flow direction on impedance eduction results2016In: 22nd AIAA/CEAS Aeroacoustics Conference, 2016, 2016Conference paper (Refereed)
    Abstract [en]

    The last twenty years have seen a large development in inverse techniques for the determination of liner impedance under grazing flow conditions, so called impedance eduction techniques. This paper contributes to a continuing e ort to gain confidence in results obtained under different acoustical excitation configurations. Many test rigs use plane wave excitation on the upstream side of the liner for determination of liner impedance including the effect of mean flow. Some studies have compared the result for downstream acoustic excitation and found that different acoustic impedances are obtained in the two cases. It is still an open question if this result is due to the application of the Ingard-Myers boundary condition or to other errors or flaws in the measurements. This paper collects data available in the literature as well as some new data to see if the trend of obtaining di erent results for upstream and downstream excitation is persistent. The Ingard-Myers boundary condition and alternative formulations published in the literature are discussed. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

  • 41.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Zhou, Lin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Acoustic Properties of an In-Duct Orifice Subjected to Bias Flow and High Level Acoustic Excitation2012In: Proceedings of the 10th International conference on Flow-Induced Vibration (& Flow-Induced Noise): FIV2012, Dublin, Ireland, 3-6 July 2012 FLOW-INDUCED VIBRATION, 2012, p. 187-193Conference paper (Refereed)
    Abstract [en]

    This paper experimentally investigates the acousticproperties of an orifice with bias flow under medium andhigh sound level excitation. The test included no bias flowand two bias speeds for three different frequencies. Experimentalresults are compared and discussed with theory.It is shown that bias flow makes the acoustic propertiesmuch more complex compared theory and with theno bias flow case, especially when velocity ratio betweenacoustic particle velocity and mean flow velocity is nearunity.

  • 42.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Zhou, Lin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    An experimental study of the effect of flow and high level acoustic excitation on the acoustic properties of perforates and orifices2013In: 20th International Congress on Sound and Vibration 2013, ICSV 2013: Volume 3, 2013, International Institute of Acoustics and Vibrations , 2013, p. 2545-2552Conference paper (Refereed)
    Abstract [en]

    Perforates are for instance used in mufflers for automotive applications and in acoustic liners for aircraft engines. In these applications they are often exposed to high level acoustic excitation in combination with grazing or bias flow. The paper is based on an experimental study of the nonlinear properties of these types of samples without mean grazing or bias flow as well as on a study of an orifice with bias flow under medium and high sound level excitation. The effect of grazing flow is discussed based on data from the literature. It is known from previous studies that high level acoustic excitation at one frequency will change the acoustic impedance of perforates at other frequencies, thereby changing the boundary condition seen by the acoustic waves. This effect could be used to change the impedance boundary conditions and for instance increase the absorption. It could obviously also pose a problem for the correct modeling of sound transmission through ducts lined with such impedance surfaces. Experimental results are compared to a quasi-stationary model. The effect of the combination of frequency components and phase in the excitation signal is studied. The bias flow tests included different flow speeds for different frequencies. The level of acoustic excitation is varied from much smaller to larger than the mean flow velocity. It is shown that bias flow makes the acoustic properties more complex compared to the no bias flow case, especially when the velocity ratio between acoustic particle velocity and mean flow velocity is near unity.

  • 43.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Zhou, Lin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Cordioli, J. A.
    Medeiros, A. A.
    Spillere, A. M. N.
    On the effect of flow direction on impedance eduction results2016In: 22nd AIAA/CEAS Aeroacoustics Conference, 2016, American Institute of Aeronautics and Astronautics Inc, AIAA , 2016Conference paper (Refereed)
    Abstract [en]

    The last twenty years have seen a large development in inverse techniques for the determination of liner impedance under grazing flow conditions, so called impedance eduction techniques. This paper contributes to a continuing e ort to gain confidence in results obtained under different acoustical excitation configurations. Many test rigs use plane wave excitation on the upstream side of the liner for determination of liner impedance including the effect of mean flow. Some studies have compared the result for downstream acoustic excitation and found that different acoustic impedances are obtained in the two cases. It is still an open question if this result is due to the application of the Ingard-Myers boundary condition or to other errors or flaws in the measurements. This paper collects data available in the literature as well as some new data to see if the trend of obtaining di erent results for upstream and downstream excitation is persistent. The Ingard-Myers boundary condition and alternative formulations published in the literature are discussed.

  • 44.
    Chowdhury, S.C.
    et al.
    BUET.
    Razzaque, M.M.
    BUET.
    Helali, M.M.
    BUET.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Assessment of noise pollution in Dhaka city2010In: 17th International Congress on Sound and Vibration (ICSV17), 2010Conference paper (Other academic)
    Abstract [en]

    Like many other mega cities of developing countries, noise pollution in Dhaka city of Bangladeshis a big concern. Here noise is produced from different sources like traffic, loudspeaker,people gathering etc. To mitigate the noise pollution in Dhaka city, the governmentof Bangladesh has recently passed a new ordinance and has modified the existing traffic controlrules. However, the condition did not improve as much as expected. Exposure to highlevel noise may cause severe stress on the auditory and nervous system of the city dwellers,particularly the children. The extreme effects e.g. deafness and mental breakdown are alsooccasionally reported. This paper reports the level of noise pollution in Dhaka city. For thispurpose noise levels have been measured at ten major locations of the city from 8 AM to 10PM during the working days. The data have been analyzed to calculate various noise parameterssuch as Leq, and Lnp. It is observed that at all the locations, the level of noise remains farabove the acceptable limit for all the time. Comparison of present results with the existingprevious results shows that noise level in the Dhaka city is increasing day by day. The papersuggests that urgent measures should be taken into consideration to control the level of noisepollution in the city and vulnerable institutions like kinder gardens, schools and hospitalsshould be located far away from the road side.

  • 45. Dolinar, A.
    et al.
    Fairbrother, R.
    Priebsch, H. -H
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Experimental investigations on the acoustic properties of some fundamental elements found in automotive exhaust mufflers2007In: Turkish Acoustical Society - 36th International Congress and Exhibition on Noise Control Engineering, INTER-NOISE 2007 ISTANBUL, 2007, p. 1361-1369Conference paper (Refereed)
    Abstract [en]

    The acoustic prediction of internal combustion engine exhaust systems is one of several important aspects needed to meet customer expectations and legislation targets. One dimensional flow duct acoustic simulation tools are already used for the prediction of the exhaust and intake orifice noise at the early stages of the engine development process. For the development of these kinds of prediction tools, experimental flow duct acoustic investigations are needed for better understanding of the acoustic behaviour of the flow ducts and for verification of the acoustic models. Flow duct acoustic measurement techniques and their application for investigating acoustic flow duct properties and verifying prediction models are described in this work. These include acoustical one-port and two-port measurements performed at zero and mean flow conditions for the evaluation of flow duct acoustic properties such as reflection coefficient, transmission loss and attenuation. From these studies it has been found that transmission loss alone is not always sufficient to verify acoustic wave transfer models. Acoustical quarter wave resonators are applied for reproducing resonant frequencies due to extended pipes into chambers. The influence of flow on these resonances has been investigated experimentally. Furthermore, the application of acoustical Helmholtz resonator models is discussed to account for some experimentally identified resonance frequencies.

  • 46. El Bardisi, M.
    et al.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Sources of noise in greater Cairo: example East Cairo2005In: 12th International Congress on Sound and Vibration 2005: ICSV 2005, 2005, p. 3481-3488Conference paper (Refereed)
    Abstract [en]

    Noise in big cities such as Cairo Egypt is an important pollutant in the modern society. Noise coming from airports, road traffic, rail traffic, power plants as well as commercial activities in the city are important contributors to the overall noise level. A noise study including measurements and predictions for noise in East Cairo coming from airport, road traffic, metro and railways was performed and analyzed. A comparison of the different sources was made and the number of affected people in the mentioned area was estimated. The dominating sources and the best mitigation to minimize the noise level was discussed and evaluated. In the analysis, some new projects was discussed individually to find its effect on noise pollution, also expectation for the coming years with the new projects and proposals where discussed. The proposed new projects include the new terminal building and runway at Cairo international airport and the proposed Heliopolis Metro Line-4 Ramsis Square - Nasr City. The analysis showed the dominating noise sources and evaluated the mentioned projects from the noise point of view. Noise out from air traffic was the dominating source of noise in East Cairo.

  • 47.
    Elnady, T.
    et al.
    KTH, Superseded Departments, Vehicle Engineering.
    Bodén, H.
    KTH, Superseded Departments, Vehicle Engineering.
    Glav, R.
    KTH, Superseded Departments, Vehicle Engineering.
    Application of the point matching method to model circumferentially segmented non-locally reacting liners2001In: 7th AIAA/CEAS Aeroacoustics Conference and Exhibit, 2001Conference paper (Refereed)
    Abstract [en]

    Acoustic liners are widely used to attenuate sound waves inside the aircraft jet engines. Previous research has proved that segmenting the liner and the positioning of the liner segments affect the attenuation characteristics of the liner. The combined effect of circumferentially segmented and non-locally reacting liners received little attention. The aim of this work is to investigate these effects, and to compare the properties of circumferentially segmented duct liners with those of uniform liners, in order to identify any potential benefits of circumferentially segmented liners. A new technique is proposed here; the point-matching method. Briefly, it is a straightforward numerical method based on a closed form ansatz, which fulfils the governing equations and is matched to the boundary conditions point-wise. A code, previously developed for automobile applications, is used to obtain the wave numbers of the different modes, from which the transmission loss for each mode can be calculated at the desired range of frequencies. An infinite cylindrical duct of diameter 40 cms was chosen to apply different non-locally (bulk) reacting liner configurations on. It was found that the existence of hard surfaces in a lined duct and their arrangement greatly affect the behavior of each mode and the energy distribution among them.

  • 48. Elnady, T.
    et al.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    A tempus experience: New curriculum in sound and vibration control in Egypt2007In: 14th International Congress on Sound and Vibration 2007, ICSV 2007, 2007, p. 2842-2849Conference paper (Refereed)
    Abstract [en]

    The reduction of noise is of environmental and strategic importance for Egypt. Noise and acoustic annoyance is considered to be a dominant source of pollution within the Egyptian community. A need to develop and strengthen education and specialization in Sound and Vibration Control was therefore identified by Ain Shams University (ASU) in Cairo. The main objective was to produce a new generation of engineers capable of performing constructive research and development in the acoustics and vibrations field. They should be able to select the appropriate hardware to accurately measure acoustic parameters, perform experiments, to come up with better solutions, analyse and simulate acoustic changes and contribute to better understanding of the noise problem. This paper describes the activities of a project funded from the European Commission through the Tempus Program. The project was implemented at Ain Shams University in cooperation with KTH (the Royal Institute of Technology) in Sweden, and ISVR (the Institute of Sound and Vibration Research) in United Kingdom. The project addressed three levels of education: undergraduate, postgraduate students and engineers already working in the industry. The activities of the project included: Improving and updating the courses at ASU - Introducing new teaching methodologies aiming at elaborating more interaction between teachers and students - Establishing a new Sound and Vibration Laboratory. The main aim is to give all students the opportunity to do measurements themselves in order to get better feeling of different phenomena - Train the current teachers and university staff on the new courses, methodologies and equipment-Offer retraining and support for engineers working in the field of sound and vibration to update their. In addition to the main goals, other advantages followed. These include the establishment of the Acoustical Society of Egypt, close collaboration between consortium member universities, and strengthening the link between Egyptian Universities, industries and research institutions.

  • 49. Elnady, T.
    et al.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Elhadidi, B.
    Validation of an Inverse Semi-Analytical Technique to Educe Liner Impedance2009In: AIAA Journal, ISSN 0001-1452, E-ISSN 1533-385X, Vol. 47, no 12, p. 2836-2844Article in journal (Refereed)
    Abstract [en]

    In this paper, the acoustic impedance of a liner is educed by a novel semi-analytical inverse technique. The liner sample is placed flush with the solid walls in a rectangular duct with grazing flow. The technique uses complex acoustic pressure measured at four positions at the wall of the duct, upstream and downstream of the lined section, and educes the impedance with a mode-matching method. Previous studies neglected grazing flow nonuniformity and the pressure discontinuity that appears at the liner-wall boundary caused by the discontinuity of the acoustic particle velocity into the wall. In the present paper, the mode-matching formulation is rederived in terms of pressure instead of velocity potential which is found to be more numerically stable. Moreover, the proposed methodology is validated with benchmark data from an experiment performed by NASA. First, the ability of the code to reproduce the pressure field for a given impedance is tested. Second, the ability to educe the correct impedance for a given pressure distribution is tested. The results of the mode-matching code are in very good agreement with the experimental data. The effect of shear flow is investigated and it can be concluded that the assumption of uniform flow is appropriate for the chosen liner, duct size, and frequency range of interest.

  • 50.
    Elnady, Tamer
    et al.
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Bodén, Hans
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    An inverse analytical method for extracting liner impedance from pressure measurements2004In: Collection of Technical Papers: 10th AIAA/CEAS Aeroacoustics Conference, 2004, Vol. 1, p. 434-450Conference paper (Refereed)
    Abstract [en]

    The in-situ method has been used for a long time as an easy, quick and direct method for measuring the acoustic impedance of locally reacting liners with and without flow. Several drawbacks and problems have been reported with the use of this method, which motivated the development of indirect methods to deduce the impedance from the measurement of the pressure field. A new inverse analytical technique is presented in this paper. The liner sample is placed inside a rectangular duct. The amplitude of the plane wave incident towards the lined section is measured using the two-microphone technique. The reflection coefficient at the exit plane is also measured using the same technique. These measured values are fed to an analytical model for sound propagation through the lined section, which is constructed using mode-matching. A minimization scheme is used to find the liner impedance value in the complex plane to match the calculated sound field to the measured one at the microphone positions already used for the two microphone measurements. The results show that the proposed technique can educe or measure the impedance to an acceptable accuracy.

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